Phallometric testing is widely considered the best psychophysiological procedure for assessing erotic preferences in men. Researchers have differed, however, on the necessity of setting some minimum criterion of penile response for ascertaining the interpretability of a phallometric test result. Proponents of a minimum criterion have generally based their view on the intuitive notion that "more is better" rather than any formal demonstration of this. The present study was conducted to investigate whether there is any empirical evidence for this intuitive notion, by examining the relation between magnitude of penile response and the agreement in diagnoses obtained in two test sessions using different laboratory stimuli. The results showed that examinees with inconsistent diagnoses responded less on both tests and that examinees with inconsistent diagnoses responded less on the second test after controlling for their response on the first test. Results also indicated that at response levels less than 1 cm(3), diagnostic consistency was no better than chance, supporting the establishment of a minimum response level criterion.